Practical surround technologies for music lovers (plus a review update). (Skeptimania).

I have lately had a chance to try out two wonderful surround-sound technologies that will just have to be of interest to those of you who have large collections of two-channel source material--be it in CD or LP form. One of these is Dolby Pro Logic II, and the other is DTS Neo:6.

To squeeze the very best performance possible out of these formats, I used two different devices: the $2,800 Yamaha RX-Z1 receiver (reviewed this issue) and the $3,400 Sunfire Theater Grand III processor (review forthcoming). After fooling around with both of them, I have concluded that while their proprietary surround and signal-processing functions have unique and often marvelous enhancement capabilities, their basic DPL II and Neo:6 modes are pretty much subjectively identical. If lower-priced receivers can perform as well, serious music lovers on a budget have much to look forward to.

There are actually two versions each of both DPL II and Neo:6. Each of those four versions is designed to do different things with different kinds of two-channel source material.

Dolby Pro Logic II (Movie) is designed to handle older two-channel motion-picture soundtracks that have been given the standard Dolby matrix production treatment. While this is no earthshaking development, what with Dolby Digital and DTS movies usually giving us five or more discrete satellite channels, DPL II (Movie) can work very well indeed with older movie soundtracks that use matrixed 4:2:4 recording/ decoding for simulated surround sound. One result is somewhat better up-front steering than what we had with the earlier Dolby Pro Logic. More importantly, however, is the way the new version extracts the 180-degree-out signals that create the "surround" channel.

Earlier DPL simply treated this extracted difference signal monophonically, sending it to two different surround-channel speaker systems. DPL II (Movie), however, works borderline miracles with that extracted signal and the result is a simulated stereo surround field that, while not able to deliver pinpoint and specific surround-channel artifacts, can do a much better job of delivering a sense of surround ambiance than earlier DPL could. This is easily audible if you listen to the surround-ambiance clicks on the Delos Surround Spectacular Dolby-matrixed test disc (DE 3179), and take my word that it shows up on matrixed movie soundtracks, too.

I have not yet had a chance to compare DPL II (Movie) to what we get with the THX emendations, which are probably superficially similar in terms of subjective impact. I reviewed the THX Ultra certified Parasound AVC-2500 too far back (in issue 83) to precisely remember its abilities with THX. However, I do have a THX Select certified Onkyo TX-DS787 on hand (reviewed in issue 86), and I hope to do some comparisons with it. I also had no way to compare its abilities to a really advanced ambiance extraction/ synthesis system, such as what we have with Lexicon's Logic 7 and Music Logic processing. I reviewed the now discontinued DC-1 quite some time ago, in issue 72, and my precise memory of that processor's stellar abilities is rather foggy.

However, I did compare it to several Yamaha theater-enhancement modes that I am very familiar with, and while in some respects it is superior to them, in others it is not so. It is not as enveloping at times as some of the Yamaha modes and may not always simulate a large-theater space as well. However, it does a better job of delivering a sense of space without also creating a faux sense of reverb from the up-front left and right channels.

Which works best for you and your movie pleasures will depend upon a multitude of factors, including room size, room shape, speaker position, listening position, and of course the program source material.

The ability of DPL II (Movie) notwithstanding, my favorite mode for movies remains one found in all four of the Yamaha units I have reviewed: "70 mm Adventure." It generates just enough lightweight ambiance to simulate a seriously large movie theater, and does so without making it sound like a cave. However, DPL-II would probably be my second choice, at least with most movies. Of course, it would probably be my first choice if I did not have a surround receiver that provided two "effects" channels up front to enhance the Yamaha modes, in addition to the regular surround channels.

In theory, DTS Neo:6 (Cinema) goes DPL II (Movie) one further. Up front, the two technologies appear to be subjectively about the same, and even further out in the room the two tend to treat matrixed movie material similarly. Both are clearly superior to the older DPL technology.

However, Neo:6 (Cinema) also sends part of the mono complement of the extracted signal to a center-back channel if you have one hooked up. Under some conditions (depending upon the room, listening position, and the location of the left/right surround speakers) it might have a leg up on DPL II (Movie). I did not notice any world-shaking advantage in my room, but there were times with some soundtracks when the center-back speakers in my set up were really pumping out a lot of sound.

OK, enough with the home-theater stuff.

For music lovers, the serious contenders will be the DPL II (Music) and Neo:6 (Music) modes. With them, the idea is to take ordinary two-channel source material and derive a faux up-front center channel, with a simulated smooth blend across the soundstage and with half-left and half-right images properly in focus and stabilized. Although similar in concept, this is somewhat different from what the movie/cinema versions do with matrixed two-channel programs. They do this in addition to simulating larger-room ambiance out in the listening area.

In most cases, standard DPL has not been able to work effectively with ordinary two-channel musical material at all. The tight steering is just not up to the task, and a collapse to the center is common with a lot of source material. The Yamaha seven-channel music modes I have played around with for some time have usually proven to be only marginally better than DPL in terms of soundstaging, unless their center levels were backed off a few dB to prevent a lateral collapse towards the middle. After that adjustment, they often work extremely well. In addition, they have always been substantially better in terms of simulating hall ambiance, however.

To make my evaluations, I used both musical source material and a series of fixed-image, pink-noise panning signals available on the before mentioned Surround Spectacular disc.

There are actually two versions of this test on the disc, with one being configured for checking out the center steering with Dolby matrixed program material and the other configured for checking out the soundstage spread, smoothness, and imaging with conventional two-channel recordings. The balance for each is somewhat different, but each test offers a sequence of white- and pink-noise signals at five locations: HARD-LEFT, HALF-LEFT, CENTER, HALF-RIGHT, and HARD-RIGHT. They do this continuously back and forth across the soundstage. They also offer continuous, smooth sweeps in addition to a five-position sequence.

The two-channel, conventional-stereo version is what we are interested in here, since that will be the most relevant to what we get when playing regular two-channel recordings. With standard, two-speaker stereo playback the levels at each of those five positions, even at half-left and half-right, should be at about the same levels--provided the listener occupies the sweet spot. The noise bursts at each location should also be well focussed, with them being uniformly strong at each of the five positions: strong / strong / strong / strong / strong. You should also experience this uniformity With good musical program material.

Unfortunately, if the listener moves some distance away from sweet-spot listening position, the smoothness of the transitions go somewhat to pot, with the sound shifting unevenly toward the closer main speaker. For example, if I move a modest distance to the right of center, the staging effect will came across as strong / very weak / weak / strong / very strong. This same kind of two-speaker soundstage skewing can also be heard with most musical source material, although it will not usually be as emphatic as it is with those test-tone noise bursts. Some speakers are designed to counteract this tendencies (the dbx Soundfield One system of a number of years ago comes to mind), and it can also be counteracted somewhat by toeing conventional speakers inward.

For my evaluation of the Dolby and DTS steering systems with two-channel music source material I primarily used two speaker/processor combinations. These were my own Allison IC-20 main speakers and a custom center speaker (plus Allison and RDL surrounds), controlled by the Yamaha RX-Z1 receiver, and then a bit later on three NHT M6 satellites and Hsu VTF-3 subwoofer (with additional NHT and RDL speakers as surrounds). The latter combination was controlled by the Sunfire Theater Grand III processor/ tuner, with three Sherbourn 1/300MB monoblocks powering the front satellite speakers and an assortment of other, smaller amps powering the surrounds.

Utilizing the center channel with either Yamaha Classical/Opera or standard Dolby Pro Logic processing (and even with the movie/cinema versions of DPL II and Neo:6), the balance at the sweet-spot listening position with this series of noise burst test signals was always: strong / weak / strong / weak / strong. In addition to being subdued in level, the half-left and half-right images were often vague in terms of stability and focus, with only hard-right, center, and hard-left sounds firmly stabilized and strong. I found that if the Yamaha's front-enhancement "effect" channels were turned on the Classical/Opera mode added a somewhat spacious characteristic up front. However, the soundstage imaging focus remained unchanged.

When listening from off axis, things got somewhat better. For example, if I sidled toward the right a couple of feet the spread was always: strong / weak / strong / strong / strong. The center steering stabilized the imaging much more effectively than what I got with only two channels.

Unfortunately, when listening from the sweet spot with a lot of complex musical material the soundstage often will partially collapse towards the center, and sometimes the collapse will be rather dramatic. The steering systems often do this with musical sources, even though they may not do it with test signals. Consequently, to make both old-style DPL and Classical/Opera steering work effectively up front it is nearly always a good idea to back the center level off about 3 dB below the normal Dolby set-up level.

I have been doing this as a matter of policy when checking out recordings in my record-review column, and it works quite well. Of course, with the Delos disc's noise-sequence test, the sweet-spot imaging will then show up as: strong / weak / weak / weak / strong. Fortunately, this far-left and far-right weighting does not cause problems with most music material. Indeed, in nearly all cases the soundstage is improved dramatically, with a smooth left-right blend, particularly when listening from off axis. At such locations, the image remains nearly as stable as what we have with the center set at the Dolby calibration level.

However, both DPL II (Music) and Neo:6 (Music) are in a position to be superior to some of those other modes when it comes to soundstage focus, spread, and stability. In addition, with the Surround Spectacular test sequence, the same results are obtained from the sweet spot as when using two speakers: strong / strong / strong / strong / strong. There was no lack of focus or image shifting at all with the Allison/Yamaha combination, nor did I detect any with the NHT/ Sunfire combination. Musical signals are equally well stabilized and spread out.

Now, to get these results with DPL II (Music), it is necessary to work with an adjustment parameter called "center width." At the lowest setting, the steering is similar to what we have with both standard DPL and DPL II (Movie) and also with the Yamaha steering modes. At the highest number, the center speaker is bypassed and you have a phantom center.

However, at an in-between setting the steered center is solidly blended with the phantom, and you get a mix that stabilizes the center, while at the same time offering up stabilized half-left and half-right images, too. I got the best results with the Dolby center width set at number 3. Neo:6 (Music) cannot be adjusted as to center width, but as best I can tell it has a fixed setting that is similar to that one.

When listening from off axis with the lowest setting of DPL II (Music) or the setting is adjusted for a modest phantom/center blend, the results are easily as good as what we get with the other steered modes, and similar results are obtained with Neo:6 (Music). If we shift the listening location to the right again we get: strong / weak/strong / strong / strong. With music, the slight weakness at the half-left location is nearly always inconsequential.

While it is debatable whether these new DPL II and Neo:6 music technologies are always superior in terms of soundstaging to what Yamaha offers With their Classical/Opera mode (with the center level reduced 3 dB to minimize center collapse), it is likely that with some musical sources they will be. I now use all three, and have decided to optimize the DPL II center-width setting at number 2, with Neo:6 being the alternate if I want a still more blended soundstage. It is not necessary to back off the center level at all with those functions selected. If I want a more lively hall acoustic, I generally opt for the Yamaha Classical/ Opera mode.

These new music-oriented Dolby and DTS technologies are also remarkable when it comes to what they can do with the surround ambiance they extract from a recording.

With the ambiance clicks on the Surround Spectacular disc, DPL II (Music) generated an almost out-of-phase characteristic from the surround channels. It was unlike anything else I have heard using those test-signal clicks. The effect is almost mysterious and when musical signals were played, the result added an uncanny three-dimensionality to the sense of large-room space in my home-listening room. The result was particularly effective with my IC-20 main speakers, because they generate a lot of side-wall reflections anyway, and those blended seamlessly with the DPL II (Music) ambiance further back into the room.

Unlike with the front soundstage, where the two technologies are fairly similar, with the surround channels Neo:6 (Music) was somewhat different from DPL II (Music). The surround ambiance had a wide feel to it, but it was more coherent and less diffuse sounding. As with the movie version, Neo:6 (Music) also makes use of the center-rear channel (if you have it hooked up), and that feed was probably responsible for the somewhat less diffuse sound from the surrounds. By now, you are probably aware that Neo:6 technology involves simulating six channels from a two-channel input.

With music, I felt that the sense of space with DPL II (Music) was a bit superior to what I detected with Neo:6. However, much will depend on the source material, the size and shape of the room, the speaker arrangement, and the listening position. From off axis, Neo:6 might have been a bit more stable in terms of soundfield consistency, but it was really hard to judge, even with the ambiance clicks.

Of course, Yamaha is noted for its soundfield enhancements, and in this case the Dolby and DTS music-mode advantages were anything but cut and dry. In most cases, the Yamaha processing came across as a bit superior, particularly with some of its concert-hall and jazz-club modes, but also with the Classical/ Opera function. DPL II and Neo:6 lack the flexibility of the Yamaha hall-ambiance palette.

To a lesser extent, the same goes for the Sunfire TG III, which has a user-adjustable Jazz mode that incorporates center steering and exhibits a remarkable ability to simulate a number of different-sized listening spaces, including a concert hall. The Sunfire also has the ability to drive a pair of up-front, side-wall-mounted effects speakers (called "side-axis" speakers), and those also imposed a degree of spaciousness and depth to the sound--and could do so even with the new Dolby and DTS modes in operation. In that respect, the Sunfire has a leg up on the Yamaha.

Speaking of adjustments, the DPL II version offers up three adjustment options that allow the user to adjust or engage several parameters to accommodate room size and shape, the listening position, and most importantly, taste.

One, called "dimension," allows one to shift the emitting soundfield further towards the front or rear of the room. A second, the aforementioned "center width" adjustment, allows one to vary the center imaging from a phantom mode to a solidly center-focussed mode, with a number of combinations in between. The most radical of these adjustment options is "panorama," which partially incorporates the surround channels into the soundstaging. The result is a wraparound effect that is not exactly my cup of tea. However, if you have been thrilled with some of the 5.1-channel musical presentations featuring "sound in the round" from all channels, the panorama mode might appeal to you. It did not appeal to me, however.

To summarize: Prior to DPL II and Neo:6, the only way an enthusiast could enjoy the benefits of high-tech, surround-sound signal enhancements with their two-channel source material was to spring for some pretty expensive DSP ambiance-synthesis hardware.

All that has changed. For the most part, Dolby Pro Logic II (Music) and DTS Neo:6 (Music) are important advances in the art of simulating a live musical performance from two-channel source material. DPL II (Music) goes Neo:6 (Music) one better, because it does allow for more adjustment parameters, although Neo:6 works terrifically right out of the box, and it also includes a center-back feed. The best thing about both is that they are now available in a large number of audio/video receivers and processors, and some of those are reasonably priced.

Indeed, this is the primarily reason why they are so revolutionary and should be of interest to every $ensible enthusiast.

Footnote to a Previous Review. I failed to mention a possible problem with the Sherbourn 1/300MB amp that I reviewed in Issue 92. As I mentioned in the review, the unit has an "auto-on" feature, meaning that it is designed to be turned on by the input signal from a preamp, similar to what we have with a lot of subwoofer amps. However, the input signal has to be reasonably strong turn the amp on and it has to remain reasonably strong if the amp is to stay that way. If after a vigorous evening of normal-level listening you decide to turn the gain down and listen at background-music levels before bedtime, you might find the amp (or amps, since you obviously will be using more than one) going to sleep prematurely. This might also happen if the amp is part of an A/V system and you are just quietly watching the news.

Under most conditions this will not be a problem, particularly if you always listen to your system at "serious" levels. However, if background music is something you also engage in, or the amps are part of an A/V installation that is also used for TV viewing at rather low levels, the anomaly might be of concern to you.

Sherbourn is upgrading future versions of the amp to have an override "on-OR-auto" switch.

--HF